1. Field of the Invention
This invention relates to an electron-emitting device and also to an electron source and an image-forming apparatus using the same as well as to a method of manufacturing the same.
2. Related Background Art
There have been known two types of electron-emitting device; the thermionic cathode type and the cold cathode type. Of these, the cold cathode type refers to devices including field emission type (hereinafter referred to as the FE type) devices, metal/insulation layer/metal type (hereinafter referred to as the MIM type) electron-emitting devices and surface conduction electron-emitting devices. Examples of FE type device include those proposed by W. P. Dyke & W. W. Dolan, "Field emission", Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, "PHYSICAL Properties of thin-film field emission cathodes with molybdenum cones", J. Appl. Phys., 47, 5248 (1976).
Examples of MIM device are disclosed in papers including C. A. Mead, "Operation of Tunnel-Emission Device", J. Appl. Phys., 32, 646 (1961).
Examples of surface conduction electron-emitting device include one proposed by M. I. Elinson, Radio Eng. Electron Phys., 10 (1965).
A surface conduction electron-emitting device is realized by utilizing the phenomenon that electrons are emitted out of a small thin film formed on a substrate when an electric current is forced to flow in parallel with the film surface. While Elinson proposes the use of SnO.sub.2 thin film for a device of this type, the use of Au thin film is proposed in G. Dittmer, "Thin Solid Films", 9, 317 (1972) whereas the use of In.sub.2 O.sub.3 /SnO.sub.2 and that of carbon thin film are discussed respectively in M. Hartwell and C. G. Fonstad, "IEEE Trans. ED Conf.", 519 (1975) and H. Araki et al., "Vacuum", Vol. 26, No. 1, p. 22 (1983).
FIG. 18 of the accompanying drawings schematically illustrates a typical surface conduction electron-emitting device proposed by M. Hartwell. In FIG. 18, reference numeral 1201 denotes a substrate. Reference numeral 1203 denotes an electroconductive thin film normally prepared by producing an H-shaped thin metal oxide film by means of sputtering, part of which eventually makes an electron-emitting region 1202 when it is subjected to a current conduction treatment referred to as "energization forming" as will be described hereinafter. In FIG. 18, the narrow film arranged between a pair of device electrodes has a length L of 0.5 to 1 mm and a width W' of 0.1 mm.
Conventionally, an electron-emitting region 1202 is produced in a surface conduction electron-emitting device by subjecting the electroconductive thin film 1203 of the device to a current conduction treatment, which is referred to as "energization forming". In an energization forming process, a constant DC voltage or a slowly rising DC voltage that rises typically at a rate of 1V/min is applied to given opposite ends of the electroconductive thin film 1203 to partly destroy, deform or transform the film and produce an electron-emitting region 1202 which is electrically highly resistive. Thus, the electron-emitting region 1202 is part of the electroconductive thin film 1203 that typically contains a fissure or fissures therein so that electrons may be emitted from the fissure. Note that, once subjected to an energization forming process, a surface conduction electron-emitting device comes to emit electrons from its electron-emitting region 1202 whenever an appropriate voltage is applied to the electroconductive thin film 1203 to make an electric current run through the device.
Known surface conduction electron-emitting devices include, beside the above described M. Hartwell's device, the one proposed in Japanese Patent Application No. 6-141670 is prepared by arranging a pair of oppositely disposed device electrodes of an electroconductive material and an independent electroconductive thin film connecting the electrodes on an insulating substrate and subjecting them to energization forming to produce an electron-emitting region. The patent document also discloses that techniques that can be used for energization forming include that of applying a pulse voltage to the electron-emitting device and the wave height of the pulse voltage is gradually raised.
There is a consistent demand for electron-emitting devices that operate uniformly and stably for electron emission when used in an image-forming apparatus so that it may be free from the problem of uneven brightness of pixels and produce stabilized images.
However, the above described Hartwell's electron-emitting device is not necessarily satisfactory in terms of uniformity and stability of electron emission.
The electron-emitting region of the device is formed by energization forming as described above but, after it is formed by energization forming, it shows an uneven and unstable profile over the entire region.
When such devices are arranged on a substrate to form an electron source of an image-forming apparatus, the electron-emitting regions of the devices will be uneven in terms of profile and electron-emitting performance as a matter of course and it will be difficult to obtain an electron source that operates uniformly and stably for electron emission. By the same token, an image-forming apparatus comprising such an electron source may not be expected to operate uniformly and stably.
There has been reports on an improved method of manufacturing a surface conduction electron-emitting device that solves the above identified problem to a considerable extent and hence can be used for manufacturing an electron source comprising such devices as well as for an image-forming apparatus comprising such an electron source. The above cited patent document also describes such an improved device.
However, in order to achieve a higher degree of applicability and adaptability for surface conduction electron-emitting devices, they have to show a further improved electron-emitting performance in terms of uniformity and stability. In particular, in the process of manufacturing an electron source by arranging a large number of surface conduction electron-emitting devices, relatively large power has to be consumed for energization forming for producing electron-emitting regions in the devices. This means that a large electric current runs through wires, which on their part resist the electric current flowing therethrough and consequently pull down the voltage until the effective voltage applied to the electron-emitting devices for energization forming significantly varies from device to device to make the devices show levels of electron-emitting performance that fluctuate considerably.
Additionally, because of the large power used for forming electron-emitting regions, they do not necessarily come out in good shape particularly from the viewpoint of electron-emitting efficiency.